Basics-Types and comparison of various touchscreen display technologies

1. Video Engineering Self Study
TOPIC: Touch-screen display technologies
Presented by
Rashmi Nambiar P.P (1RV13TE040)
Sharmila Kishore Kumble (1RV13TE046)
SEM VI

2. Introduction
 A touchscreen is an input device normally layered on the top of an electronic visual display of
an information processing system. A user can give input or control the information processing
system through simple or multi-touch gestures by touching the screen.
 Some touchscreens use ordinary or specially coated gloves to work while others use a special
stylus/pen only. The user can use the touchscreen to react to what is displayed and to control
how it is displayed.
 The first touchscreen is considered to have been of capacitive type invented by
E.A. Johnson in 1965 at the Royal Radar Establishment
in Malvern, United Kingdom.
April 30, 2016 RVCE 2015-16, VE 2

3. Major components of touchscreen
 Touch Sensor : Glass panel with a touch responsive surface
having an electrical current or signal going through it and causes
a voltage or signal change which is used to determine the
location.
 Controller : Small PC card connects between the touch sensor
and the PC.
 Software Driver : Software allows the touch screen and computer
to work together.
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4. Types of touchscreen display technologies
There are four main touchscreen technologies:
1) Resistive
2) Capacitive
3) Surface Acoustic Wave
4) Infrared
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5. Resistive type
 Solid glass substrate
 PET (Polyethylene terephthalate)- a flexible polyester membrane
 Hardcoat- makes the surface of PET more wear-resistant
 Because of the air gaps, a resistive touch screen has four reflecting surfaces- S1 through S4
 Surfaces S1 and S4 each reflect 4% of the incident light (normal for PET and glass), while
surfaces S2 and S3 each reflect around 5% (higher because of the ITO). Surface S5 reflects
about 2%
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6. Two alternative treatments that can be applied to resistive touch screens to reduce
their reflectivity are as follows:
 In the first treatment, touch-screen surfaces S1 through S4 and the LCD surface S5
are coated with anti-reflective (AR) material.
 AR coatings are sometimes called "index-matching films" because one of their
functions is to reduce the effect of the difference in index of refraction between air
(1.0) and glass (1.5), PET (1.6) or ITO (2.0).
 Another name for AR coatings is "quarter-wavelength films." If the thickness of an
AR coating is exactly one-quarter (or an odd multiple of one quarter) of the
wavelength of light, destructive optical interference takes place and some of the
reflections cancel each other out.
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7.  Second treatment method- Using a circular polariser to block reflection
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8. Types of Resistive Touchscreens
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a) 4-Wire resistive technology b) 5-Wire resistive technology

9.  Advantages of resistive touch screens:
• Can be activated with virtually any object (finger, stylus, gloved hand, pen, etc.)
• Has tactile feel
• Lowest cost touch technology
• Low power consumption
• Resistant to surface contaminants and liquids (dust, oil, grease, moisture)
 Disadvantages:
• Lower image clarity compared to other touch technologies
• Outer polyester film is vulnerable to damage from scratching, poking and sharp
objects.
• The analog system is susceptible to drift, so the user may have to recalibrate the
touch panel from time to time.
• The ITO material used for the conductors is brittle causing cracks on repeated use.
This leads to deadspots on the screen
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10. Capacitive Touchscreen
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• It consists of a transparent electrode layer is placed on top of a glass panel.
• When an exposed finger touches the monitor screen some of the electrical charge transfers
from the screen to the user.
• This decreases the capacitance that is detected by sensors located at the four corners of the
screen, allowing the controller to determine the touch point.

11. April 30, 2016 RVCE 2015-16, VE 11
There are two types of capacitive touchscreens:
1. Surface Capacitive: Only one side of the insulator is coated with a conductive layer. A small
voltage is applied to the layer, resulting in a uniform electrostatic field. When a conductor,
such as a human finger, touches the uncoated surface, a capacitor is dynamically formed.
2. Projected Capacitive: They are made up of a matrix of rows and columns of conductive
material, layered on sheets of glass obtained by etching. The electromagnetic field projects
above the plane of the conductive sensor layer. They use two layers of conductors made of
transparent ITO, separated by an insulator such as a thin sheet of glass. The difference of
capacitance is that the separate conductors are scanned in rapid sequence, so that all the
possible intersections are measured many times per second.

12. April 30, 2016 RVCE 2015-16, VE 12
Advantages of capacitive touch screens:
• Multi-touch (two-touch)
• Excellent image clarity
• Projected Capacitive more resistant to scratching than Surface Capacitive
• Resistant to surface contaminants and liquids (dust, oil, grease, moisture)
 Disadvantages:
• Requires bare finger or capacitive stylus for activation
• Sensitivity to EMI/RFI

13. Infrared type
 Infrared technology consists of infrared LEDs (Light emitting diode) and light sensors that are
placed on the perimeter of the bezel (frame). LEDs transmit beams of light that run parallel to
the assigned light sensor create a light grid. Anything that disrupts the light or reduces the light
such as a finger or stylus will register a touch.
 A microchip inside the screen can calculate where we touch by seeing which beams are
interrupted.
 Works best with larger screens
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14. Advantages of infrared touch screens:
 Highest image clarity and light transmission of all touch technologies
 Unlimited “touch-life”
 Impervious to surface scratches
Disadvantages:
 Accidental activation may occur because the infrared beams are actually above the glass
surface
 Dust, oil, or grease buildup on screen or frame could impede light beam causing
malfunction
 Sensitive to water, snow, rain
 May be sensitive to ambient light interference – not suitable outdoors
 Higher cost
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15. Surface Wave Acoustic
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• Surface Acoustic Wave (SAW) technology uses ultrasonic waves that pass over the touch
screen panel.
• When the panel is touched, a portion of the wave is absorbed. The change in the ultrasonic
waves registers the position of the touch event and sends this information to the controller for
processing.
• SAW touch screen technology is used in ATMs, Amusement Parks, Gaming Environments,
Industrial Control Rooms etc.

16. April 30, 2016 RVCE 2015-16, VE 16
 Advantages of Surface Acoustic Wave Touchscreen
• Very High Light Transmission
• Excellent Durability
• High Resolution
• Fast Touch Response
• Finger or Gloved-Hand Operation
 Disadvantages of Surface Acoustic Wave Touchscreen
• Must be touched by finger, gloved hand, or soft-tip stylus. Something hard like a pen won't
work
• Not completely sealable, can be affected by large amounts of grease, water, or dirt on the
touchscreen

17. Comparison
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Resistive Infrared SAW Capacitive
Touch
Resolution
High High Average High
Clarity Average Good Good Good
Operation Finger or
Stylus
Finger or
Stylus
Finger or Soft-
tipped Stylus
Finger only
Durability Can be
Damaged by
Sharp Objects
Highly Durable Susceptible to
Dirt and
Moisture
Highly durable

18. References
[1] Mudit Ratana Bhalla, Anand Vardhan Bhalla, “Comparative Study of Various
Touchscreen Technologies”, International Journal of Computer Applications, (0975
– 8887)Volume 6– No.8, September 2010
[2] Geoff Walker, “The ultimate outdoor-readable touch-screen display”, GD- Itronix
DynaVue Display Technology
[3] “The technology within touch panels”, by Epec Engineered Technologies
[4] Holsinger, Erik. (1994) “How Multimedia Works”, Emeryville, CA: Ziff-Davis
Press.
[5] Wilson, Tracy, “HowStuffWorks -Multi-touch Systems".
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19. RVCE 2015-16, VE 19April 30, 2016